1. Field of Art
The present invention relates to a distance measuring equipment (referred herein sometimes to “DME”) installed at a ground station to transmit replies to interrogations received from aircraft measuring the distance relative to the ground, and a distance measuring equipment (DME) monitor system.
2. Description of Relevant Art
The DME is used for measurement of distance between aircraft and the ground (refer to Japanese Patent Application Laid-Open Publication No. 2008-286683).
FIG. 1 illustrates a DME 1a installed on the ground, and adapted to receive a sequence of interrogations transmitted from an interrogator 20 mounted on aircraft 2. The DME 1a is adapted to transmit to the interrogator 20 on aircraft 2 a sequence of replies responding to interrogations the DME 1a has received. The aircraft 2 can make use of a round-trip time required for signal transmission and reception, for measurement of distance between the aircraft and a reference location on the ground (e.g., location where the DME 1a is installed).
As shown in FIG. 2, the DME 1a has a transponder 12 configured for transmission of replies to interrogations received from aircraft 2. As illustrated in FIG. 3(a) and FIG. 3(b), the (interrogator 20 on) aircraft 2 transmits (at a time t1) an interrogation P1. This is received by the (transponder 12 in) DME 1a, which responds it by transmitting a reply P2 with a precise preset delay of time Td. The aircraft 2 can receive (at a time t2) the reply P2 from the (transponder 12 in) DME 1a, and calculate a round-trip time T (=t2−t1) from (pulse rise time t1 at the) transmission of interrogation P1 to (pulse rise time t2 at the) reception of reply P2, for use to determine a position of the aircraft 2.
Interrogations P1 and replies P2 are each prescribed, i.e., formatted in advance to a prescript of style. Simply to reception of an interrogation P1 compliant with the prescript, the transponder 12 responds with transmission of a reply P2. Interrogations P1 as well as replies P2 are each composed of a pair of pulses referred herein to as a pulse pair or twin pulses. In the example of mode illustrated in FIGS. 3(a) and 3(b), interrogations P1 as well as replies P2 are each composed of a pair of pulses that have a 3.5 μs pulse width, and a 12 μs pulse spacing or interval.
Referring to FIG. 2, the DME 1a includes: an antenna 11; the transponder 12 being composed of first and second transponders 12a and 12b of an identical configuration; a monitoring processor 13 being composed of first and second monitoring processors 13a and 13b; a switching circuit 14; and a controller 15 for controlling the transponder 12 and the monitoring processor 13.
The monitoring processor 13a and 13b are configured to generate a pseudo interrogation identical in format of style to those interrogations P1 compliant with the above-noted prescript, to output to the transponder 12. The pseudo interrogation being identical in format of style to interrogations P1 is input from the monitoring processor 13, through the switching circuit 14, to the transponder 12, where it is processed like a normal interrogation P1 (that the transponder 12 has received via the antenna 11 and the switching circuit 14), without checks if it is any pseudo interrogation, to generate a reply P2 thereto.
Accordingly, the transponder 12 works for generation of a reply P2 responding to a normal interrogation P1 received from aircraft 2, and for generation of a reply P2 responding to a pseudo interrogation received from the monitoring processor 13. The switching circuit 14 is adapted, with the former P2 input thereto from the transponder 12, to work for a switching to transmit the input reply P2 via the antenna 11 to aircraft 2, and with the latter P2 input thereto, to work for a switching to output the input reply P2 to the monitoring processor 13.
The reply P2 responding to pseudo interrogation is input from the switching circuit 14 to the monitoring processor 13, whereby the processor 13 is given information, such as on if the reply P2 is input thereto and on the timing of input, and employs this for a monitoring to determine whether or not the transponder 12 is in a conforming performance to transmit a reply P2 in response to a normal interrogation P1 it has received.
The DME 1a is configured in compliance with associated prescripts specifying, among others besides the format of style, frequencies of interrogations P1 and replies P2 to be processed, and transmission rates, as well, in order to implement transmission of a reply P2 in response to reception of a prescript-compliant interrogation P1. For signals to be processed at DME transponders, prescripts are standardized. For enhancement in integrity of DME performance, transponders are required to have a specified integrity, cf. “Minimum Performance Specification for Ground Distance-Measuring Equipment (DME) ED-57”, EUROCAE, 1986.
The transponder 12 of DME 1a is subject to a performance verification to determine whether or not the transponder 12 meets a required integrity of performance. The performance verification of transponder 12 needs use of dedicated jigs, facilities, etc. Additionally, it spends too much time, costing dearly.
Likewise, conventional DME's have been subject to a performance verification of transponder needing dedicated jigs and facilities, spending too much time, costing dearly.
It is an object of the present invention to provide a distance measuring equipment, and a distance measuring equipment monitor system, permitting a facilitated verification of transponder performance, allowing for an enhanced efficiency of performance verification.